This invention relates to multiplexer-type structures for use in making controllable interconnections in integrated circuits such as programmable logic devices.
Pedersen et al. U.S. Pat. No. 5,241,224 teaches that instead of a large cross-point type switch capable of connecting any input to the switch to any output from the switch in order to route signals through an integrated circuit such as a programmable logic device, a more economical arrangement of multiplexers can often be used to provide a sufficient subset of such signal routing capability. In a programmable logic device, for example, other programmable circuitry associated with the communication network selects which of the multiplexer inputs is actually enabled when the device is used. The objective of the '224 patent is to provide enough interconnection capability so that the signal routing required in most applications of the circuit can be accomplished without unduly burdening the circuit with large amounts of interconnection capability that will be unused in a large number of cases. To accomplish this objective the '224 patent teaches connecting each input signal conductor to two different multiplexers, and avoiding connection of any two input conductors to the same two multiplexers. The '224 patent also teaches that the input conductors and the multiplexers they feed should preferably form an acyclic chain.
Although the multiplexer connection arrangements taught in the '224 patent have been highly successful, it has been found that those arrangements may have one or more disadvantages in some situations. For example, the '224 patent multiplexer connection arrangements are relatively complicated to select and implement. In other words, it may be relatively difficult to design a multiplexer connection arrangement that satisfies the '224 patent criteria. And because the '224 patent criteria tend to produce multiplexer connection arrangements that are highly irregular or random, substantial effort may be required to physically implement them in the integrated circuit. There is little or no repetition in the '224 patent multiplexer connection arrangements that can be relied on to help speed the detailed circuit design process. All of these factors tend to increase the manufacturing cost of the integrated circuit.
Another possible disadvantage of the '224 patent multiplexer connection arrangements is that they may call for connection of two or more adjacent input conductors to the same multiplexer. This may further complicate the task of physically implementing the circuit, and it may even prevent placing the input conductors as close together as would otherwise be possible and desirable in order to make the most efficient use of the area of the integrated circuit.
In view of the foregoing, it is an object of this invention to provide improved multiplexer-based interconnection structures or communication networks for use in integrated circuits such as programmable logic devices.
It is a more particular object of this invention to provide integrated circuit interconnection structures or communication networks which make use of multiplexers and which have most or all of the advantages of the '224 patent arrangements without any of the above-mentioned possible disadvantages of the '224 patent arrangements.